Measurement of the CP asymmetry in $D^0\to\pi^+\pi^-\pi^0$ decays at Belle II

Abstract KEK-PREPRINT-2025-17 We measure the time- and phase-space-integrated $C\!P$ asymmetry $A_{C\!P}$ in $D^0\to\pi^+\pi^-\pi^0$ decays reconstructed in $e^+e^-\to c\bar c$ events collected by the Belle II experiment from 2019 to 2022. This sample corresponds to an integrated luminosity of 428 fb$^{-1}$. We require $D^0$ mesons to be produced in flavor-conserving $D^{*+}\to D^0\pi^+$ decays to determine their flavor at production. Control samples of $D^0\to K^-\pi^+$ decays are used to correct for reconstruction-induced asymmetries. The result, $A_{C\!P}(D^0\to\pi^+\pi^-\pi^0)=(0.29\pm0.27\pm0.13)\%$, where the first uncertainty is statistical and the second systematic, is consistent with conservation of $C\!P$ symmetry and is the most precise determination to date.
Tags Run 1
Working group Charm
Principal authors @  Giulia Casarosa, Ludovico Massaccesi
Reference accepted by PRD, DOI: https://doi.org/10.1103/4yv7-1h85
Links arXiv:2510.21224, Inspire, PRD
Bibtex 
@article{Belle-II:2025zqj,
    author = "Abumusabh, M. and others",
    collaboration = "Belle-II",
    title = "{Measurement of the $CP$ asymmetry in $D^0\toπ^+π^-π^0$ decays at Belle II}",
    eprint = "2510.21224",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II preprint 2025-018, KEK preprint 2025-17",
    month = "10",
    year = "2025"
}